By Ben Orlin

Teacher compensation has become a key part of the public debate over American schools. U.S. Education Secretary Arne Duncan has sounded the war-horns for higher salaries. New Jersey governor Chris Christie wrestles with unions over benefits. When she was chancellor of the D.C. public school system, Michelle Rhee fought to remake teacher pay scales, en route to becoming the most divisive figure in American education. And whatever your agenda, the salary gap between public and private threatens to rewrite the storyline. If public schools pay too little, why do privates pay even less? On the other hand, with better-paying public-school jobs available, why do so many teachers accept lower salaries in order to go private?

Some conclude that public-school teachers must be overpaid. Teachers’ unions, they contend, possess an unfair advantage. Through lobbying and campaign contributions, they get to pick who sits across the bargaining table from them. No private union has that power. This perverse scenario, they claim, allows teachers to negotiate lavish pensions and above-market wages. (Never mind that teachers earn 30 percent less per year than other college graduates.)

The opposite interpretation is that private-school teachers must be underpaid. Private schools, some point out, suffer higher teacher turnover among early-career teachers: 24 percent of private-school teachers are in their first three years of teaching, compared with 13 percent of public-school teachers. And on their way out the door, two-thirds cite low salary as a reason for leaving. So private schools’ stingy wages must be failing to draw and retain good teachers. (Never mind that their students seem to do just fine.)

Both of these positions overlook the simplest explanation. The labor markets are just plain different—and those differences may hold meaningful lessons.

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The first main difference is licensure. Public education has more jobs to fill (87 percent of all teaching jobs nationwide) and fewer people to fill them. That’s because whereas private schools hire whomever they want, state laws require public schools to hire only licensed teachers.

That means public schools have greater demand for workers, and smaller supply. Any economist—really, anyone who’s slept through an Econ 101 lecture—can tell you what comes next. In order to fill their staffs, public schools will need to offer a more attractive wage. They aren’t splurging, any more than private schools are scrimping. It’s just the market—two different markets, in fact—at work.

This brings us to the second main difference between publics and privates, and to the crux of the paradox. How can private schools pay their teachers less, yet offer an education for which parents gladly spend tens of thousands per year? The answer is right there in the question.

Class sizes are smaller—a 12:1 student-to-teacher ratio, compared with 16:1 at public schools. There’s also less red tape—private teachers answer to principals and parents, rather than to principals, parents, and three meddling levels of government. And the families at private schools are, quite literally, invested in education. A national survey of teachers, asking them about the problems their schools face, paints a vivid contrast:

Whereas many public school teachers spend their days leaping over hurdles, private school teachers actually get to—just imagine!—teach. This explains why they’re twice as likely to hold Ph.D.s, despite earning $6,500 less per year than Ph.D.s at public schools. It also explains why 21 percent of private school teachers have two decades or more of experience—virtually the same ratio as in public schools. They stay because they enjoy the work.

Obviously, teachers care about what they’re paid. But they also care about what they’re paid to do. Some will even take a lower salary if it means a chance to do their jobs right.

The biggest lesson public education can draw from the salary gap isn’t to cut wages, or quash unions, or hold open auditions for unlicensed teachers. The lesson, in fact, has little to do with salaries at all. The moral is that not all teaching jobs are alike. Different school environments make for radically different work, and many teachers find private schools offer a more rewarding experience. Attracting and retaining teachers, then, means more than just raising salaries. It means taking disciplinary obstacles and bureaucratic nonsense out of teachers’ paths.

The lesson, in short, is that you’ll attract more teachers by letting them teach.